Electronic device

ABSTRACT

An electronic device, such as a thin-film transistor, includes a semiconducting layer formed from a semiconductor composition. The semiconductor composition comprises a polymer binder and a small molecule semiconductor. The semiconducting layer has been deposited on an alignment layer that has been aligned in the direction between the source and drain electrodes. The resulting device has increased charge carrier mobility.

BACKGROUND

The present disclosure relates to thin-film transistors (TFTs) and/orother electronic devices comprising a semiconducting layer and analignment layer. The alignment layer is used to increase the chargecarrier mobility of the transistor and/or electronic device. Highmobility and excellent stability may be achieved.

TFTs are generally composed of, on a substrate, an electricallyconductive gate electrode, source and drain electrodes, an electricallyinsulating gate dielectric layer which separate the gate electrode fromthe source and drain electrodes, and a semiconducting layer which is incontact with the gate dielectric layer and bridges the source and drainelectrodes. Their performance can be determined by the field effectmobility (also referred to as the charge carrier mobility) and thecurrent on/off ratio of the overall transistor. High mobility and highon/off ratio are desired.

Organic thin-film transistors (OTFTs) can be used in applications suchas radio frequency identification (RFID) tags and backplane switchingcircuits for displays, such as signage, readers, and liquid crystaldisplays, where high switching speeds and/or high density are notessential. They also have attractive mechanical properties such as beingphysically compact, lightweight, and flexible.

Organic thin-film transistors can be fabricated using low-costsolution-based patterning and deposition techniques, such as spincoating, solution casting, dip coating, stencil/screen printing,flexography, gravure, offset printing, ink jet-printing, micro-contactprinting, and the like. To enable the use of these solution-basedprocesses in fabricating thin-film transistor circuits, solutionprocessable materials are therefore required. However, organic orpolymeric semiconductors formed by solution processing tend to sufferfrom limited solubility, air sensitivity, and especially lowfield-effect mobility.

It would be desirable to develop new techniques to increase the fieldeffect mobility of such semiconductors.

BRIEF DESCRIPTION

The present application discloses, in various embodiments, electronicdevices and processes for making such electronic devices. The electronicdevices include a semiconducting layer and an alignment layer. It isbelieved that the alignment layer induces microscopic and/or macroscopicalignment of the semiconducting layer.

Disclosed in embodiments is an electronic device comprising: asemiconducting layer comprising a small molecule semiconductor and apolymer binder; and an alignment layer in contact with the semiconductorlayer.

The alignment layer may have a thickness of from about 0.2 nanometers toabout 1 micrometer.

The alignment layer may be formed from a polyimide, a poly(vinylcinnamate), an azobenzene polymer, a styrene-based polymer, or anorganosilane agent of Formula (A):

(L)_(t)-[SiR_(m)(R′)_(4-m-t)]_(v)  Formula (A)

wherein R is alkyl or aryl; R′ is halogen or alkoxy; m is an integerfrom 1 to 4; L is a linking atom; t is 0 or 1; and v indicates thenumber of trisubstitutedsilyl groups on the linking atom.

In embodiments, the small molecule semiconductor may be a liquidcrystalline compound.

The small molecule semiconductor may have the structure of Formula (I):

wherein each R₁ is independently selected from alkyl, substituted alkyl,alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano, and halogen; m and n are the number of R₁sidechains on their respective phenyl or naphthyl ring, and areindependently an integer from 0 to 6; X is selected from the groupconsisting of O, S, and Se; and a, b, and c are independently 0 or 1.

The small molecule semiconductor could have the structure of Formula(II):

wherein R₂ and R₃ are independently selected from alkyl, substitutedalkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano, and halogen.

The small molecule semiconductor may have the structure of Formula(III):

wherein R₈, and R₉ are independently alkyl or substituted alkyl; andeach Ar is independently an arylene or heteroarylene group.

The small molecule semiconductor could have the structure of Formula(IV):

wherein R₄ and R₅ are independently selected from alkyl, substitutedalkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano, and halogen; and j and k areindependently an integer from 0 to 6.

The small molecule semiconductor may have the structure of Formula (V):

wherein R₆ and R₇ are independently selected from alkyl, substitutedalkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano, and halogen; and p and q areindependently an integer from 0 to 4.

Alternatively, the small molecule semiconductor may have the structureof Formula (VI):

wherein R₁₀ and R₁₁ are independently selected from alkyl, substitutedalkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano, and halogen; and a, b, and c areindependently 0 or 1.

The polymer binder may be a styrene-based polymer or an arylamine-basedpolymer. In specific embodiments, the polymer binder is polystyrene,poly(α-methyl styrene), poly(4-methyl styrene), poly(alpha-methylstyrene-co-vinyl toluene), poly(styrene-block-butadiene-block-styrene),polystyrene-block-isoprene-block-styrene), poly(vinyl toluene), aterpene resin, poly(styrene-co-2,4-dimethylstyrene),poly(chlorostyrene), poly(styrene-co-α-methyl styrene),poly(styrene-co-butadiene), polycarbazole, a polytriarylamine, orpoly(N-vinylcarbazole). The polymer binder may alternatively be astyrene-based polymer having a weight average molecular weight of fromabout 40,000 to about 2,000,000.

The weight ratio of the small molecule semiconductor to the polymerbinder may be from about 99:1 to about 1:3.

Also disclosed in embodiments is a thin film transistor comprising: agate electrode, a source electrode, a drain electrode, a gate dielectriclayer, a semiconductor layer, and an alignment layer. The sourceelectrode and the drain electrode define a transistor channel. Thesemiconducting layer comprises a small molecule semiconductor and apolymer binder. The alignment layer is in contact with the semiconductorlayer; wherein the small molecule semiconductor is aligned along thedirection of the transistor channel direction.

The transistor comprising the alignment layer may have a field-effectmobility of at least 0.8 cm²/V·sec.

In particular embodiments, the alignment layer is located between thesemiconductor layer and the gate dielectric layer.

Also disclosed is a method for forming an electronic device. Generally,the alignment layer, semiconducting layer, source electrode, and drainelectrode are deposited on the substrate in whatever order is needed toform the desired device. The alignment layer is aligned in a transistorchannel direction between the source electrode and the drain electrodeat some point during the formation of the electronic device. Thesemiconducting layer is deposited on the alignment layer after thisalignment process. The source electrode and the drain electrode define atransistor channel.

The alignment layer may be aligned by rubbing the aligning layer in thetransistor channel direction, between the source electrode and the drainelectrode. Alternatively, the alignment layer is formed from apolyimide, a poly(vinyl cinnamate), or an azobenzene polymer; and thealignment layer is aligned by irradiating the alignment layer withlinearly polarized light.

In particular embodiments, the alignment layer is deposited upon adielectric layer, the alignment layer is subsequently aligned, and thesemiconducting layer is subsequently deposited upon the alignment layer.

Also disclosed in embodiments is an electronic device comprising: asource electrode and a drain electrode; an alignment layer having afirst surface and a second surface; and a semiconducting layer depositedon a first surface of the alignment layer. The first surface was alignedin a direction between the source electrode and the drain electrodeprior to the deposition of the semiconducting layer.

These and other non-limiting characteristics of the disclosure are moreparticularly disclosed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawings, which arepresented for the purposes of illustrating the exemplary embodimentsdisclosed herein and not for the purposes of limiting the same.

FIG. 1 is a diagram of a first embodiment of a TFT according to thepresent disclosure.

FIG. 2 is a diagram of a second embodiment of a TFT according to thepresent disclosure.

FIG. 3 is a diagram of a third embodiment of a TFT according to thepresent disclosure.

FIG. 4 is a diagram of a fourth embodiment of a TFT according to thepresent disclosure.

FIG. 5 is a perspective view showing certain aspects of the alignmentlayer.

FIG. 6 is a diagram showing a fifth embodiment of a TFT according to thepresent disclosure.

DETAILED DESCRIPTION

A more complete understanding of the components, processes andapparatuses disclosed herein can be obtained by reference to theaccompanying drawings. These figures are merely schematicrepresentations based on convenience and the ease of demonstrating thepresent disclosure, and are, therefore, not intended to indicaterelative size and dimensions of the devices or components thereof and/orto define or limit the scope of the exemplary embodiments.

Although specific terms are used in the following description for thesake of clarity, these terms are intended to refer only to theparticular structure of the embodiments selected for illustration in thedrawings, and are not intended to define or limit the scope of thedisclosure. In the drawings and the following description below, it isto be understood that like numeric designations refer to components oflike function.

The modifier “about” used in connection with a quantity is inclusive ofthe stated value and has the meaning dictated by the context (forexample, it includes at least the degree of error associated with themeasurement of the particular quantity). When used in the context of arange, the modifier “about” should also be considered as disclosing therange defined by the absolute values of the two endpoints. For example,the range of “from about 2 to about 10” also discloses the range “from 2to 10.”

The term “comprising” is used herein as requiring the presence of thenamed component and allowing the presence of other components. The term“comprising” should be construed to include the term “consisting of”,which allows the presence of only the named component, along with anyimpurities that might result from the manufacture of the namedcomponent.

The present disclosure relates to electronic devices, such as thin filmtransistors (TFTs), comprising an alignment layer and a semiconductinglayer comprising a polymer binder and a small molecule semiconductor.The alignment layer is used to increase the field effect mobility of theelectronic device.

FIG. 1 illustrates a bottom-gate bottom-contact TFT configurationaccording to the present disclosure. The TFT 10 comprises a substrate 16in contact with the gate electrode 18 and a gate dielectric layer 14.The gate electrode 18 is depicted here atop the substrate 16, but thegate electrode could also be located in a depression within thesubstrate. The gate dielectric layer 14 separates the gate electrode 18from the source electrode 20, drain electrode 22, and the semiconductinglayer 12. The semiconducting layer 12 runs over and between the sourceand drain electrodes 20 and 22. The semiconductor has a channel lengthbetween the source and drain electrodes 20 and 22. An alignment layer 13is located between the dielectric layer 14 and the semiconducting layer12. A first surface 15 of the alignment layer directly contacts thesemiconducting layer 12. A second surface 17 of the alignment layerdirectly contacts the dielectric layer 14.

FIG. 2 illustrates another bottom-gate top-contact TFT configurationaccording to the present disclosure. The TFT 30 comprises a substrate 36in contact with the gate electrode 38 and a gate dielectric layer 34. Analignment layer 33 is placed on top of the gate dielectric layer 34. Asecond surface 37 of the alignment layer directly contacts thedielectric layer 34. The semiconducting layer 32 is deposited upon afirst surface 35 of the alignment layer 33. The semiconducting layeralso separates the dielectric layer 34 from the source and drainelectrodes 40 and 42.

FIG. 3 illustrates a bottom-gate bottom-contact TFT configurationaccording to the present disclosure. The TFT 50 comprises a substrate 56which also acts as the gate electrode and is in contact with a gatedielectric layer 54. An alignment layer 53 is placed on top of the gatedielectric layer 54. The source electrode 60, drain electrode 62, andsemiconducting layer 52 are located atop the alignment layer 53. A firstsurface 55 of the alignment layer directly contacts the semiconductinglayer 52.

FIG. 4 illustrates a top-gate top-contact TFT configuration according tothe present disclosure. The TFT 70 comprises a substrate 76. Analignment layer 73 is located upon the substrate 76 between thesubstrate 76 and the semiconducting layer 72. A first surface 75 of thealignment layer directly contacts the semiconducting layer 75. A secondsurface 77 of the alignment layer directly contacts the substrate 76.The alignment layer is also in contact with the source electrode 80 andthe drain electrode 82. The semiconducting layer 72 runs over andbetween the source and drain electrodes 80 and 82. The gate dielectriclayer 74 is on top of the semiconducting layer 72. The gate electrode 78is on top of the gate dielectric layer 74 and does not contact thesemiconducting layer 72.

It has been found that using the alignment layer increases the fieldeffect mobility dramatically. It is believed that this increase is dueto the alignment of the semiconductor layer along the transistor channeldirection which is induced by the alignment layer. The chemicalcomposition of the alignment layer itself is not necessarilysignificant. FIG. 5 is a perspective view of an embodiment similar tothat of FIG. 1. The alignment layer 103 is visible. A source electrode110 and a drain electrode 112 are located upon the alignment layer. Thedirection between the source electrode 110 and the drain electrode 112is indicated by arrow 105, or put another way arrow 105 indicates adirection from the source electrode 110 to the drain electrode 112. Thesurface of the alignment layer is aligned in the direction indicated byarrow 105. This direction can also be referred to as the transistorchannel direction. In a cyclic electrode where one electrode issurrounded by the other electrode with a semiconducting layer having anannular shape between the two electrodes, the transistor channeldirection would be in the radial direction. This alignment occurs atleast in the transistor channel between the source electrode and thedrain electrode, and is indicated by lines 120. For example, thealignment begins at one of the electrodes and ends at one of theelectrodes.

This alignment effect can be achieved by mechanical means or by indirectmeans. An example of a mechanical treatment is by rubbing the surface ofthe alignment layer upon which the semiconducting layer will bedeposited. This mechanical rubbing may be performed with a rubbing clothcomprising a material such as rayon, cotton, or polyamide. The rubbingcloth can be wound around a roller which is used to perform the rubbing.An example of an indirect treatment is irradiating the alignment layerwith linearly polarized light between the source and drain electrodes.The alignment treatment should be performed, at a minimum, in the areadirectly between the source and drain electrodes that corresponds to thesemiconductor channel.

A first surface of the alignment layer directly contacts thesemiconducting layer. Without being bound by theory, it is believed thatthe alignment treatment induces macroscopic alignment of the smallmolecule semiconductor material in the semiconducting layer, and mayalso reduce grain boundaries in the semiconducting layer. These effectscan enhance charge carrier mobility.

The alignment layer may be formed from any suitable material. Inembodiments, the alignment layer is formed from a polyimide, poly(vinylcinnamate), a styrene-based polymer, an azobenzene polymer, compoundscomprising a cinnamate group or an azobenzene group, or the like. Acinnamate group has the structure C₆H₅—CH═CH—COO—. An azobenzene groupcontains an azo group (—N═N—) with each nitrogen atom being bonded to aphenyl group, the azobenzene group attaching to another atom through oneof the phenyl groups.

In other embodiments, the alignment layer is formed from an organosilaneagent of Formula (A):

(L)_(t)-[SiR_(m)(R′)_(4-m-t)]_(v)  Formula (A)

wherein R is alkyl or aryl; R′ is halogen or alkoxy; m is an integerfrom 1 to 4; L is a linking atom; t is 0 or 1, and indicates whether alinking atom is present; and v indicates the number oftrisubstitutedsilyl groups on the linking atom. The sum of (m+t) isnever greater than 4. When t is 0, v is automatically 1. Exemplaryorganosilane agents of Formula (A) include hexamethyldisilazane (HMDS)(L=NH, t=1, R=methyl, m=3, v=2) and octyltrichlorosilane (OTS-8) (t=0,R=octyl, m=1, R′=chloro, v=1). Other exemplary organosilane agentsinclude dodecyltrichlorosilane, phenyltrichlorosilane,methyltrimethoxylsilane, phenylmethyldimethoxysilane,phenylmethyldichlorosilane, phenyltrimethoxysilane, and the like.

The alignment layer has a thickness or depth of from about 0.2nanometers (for example, a self-assembled monolayer) to about 1micrometers, including from about 0.2 nanometers to about 500nanometers. The alignment layer can be formed using methods known in theart for the particular material, for example spin coating, dip coating,vapor evaporation, self-assembling, chemically grafting from thedielectric or substrate surfaces, and the like. It should be noted thatthe alignment layer is shown, for example in FIG. 1 as being an entirelayer 13 that separates the dielectric layer 14 from the semiconductinglayer 12. This type of construction may be easier for manufacturingpurposes. However, the alignment effect can also be achieved if, as seenfor example in FIG. 6, the alignment layer 13 is present only in thechannel between the source electrode 20 and the source electrode 22.

The semiconducting layer directly contacts the alignment layer. Thesemiconducting layer may be formed from a semiconducting compositionthat comprises a polymer binder and a small molecule semiconductor. Asemiconducting layer formed from the composition is very stable in airand has high mobility. These semiconductor compositions are useful forforming layers in electronic devices, such as thin film transistors(TFTs).

The small molecule semiconductor may have the structure of Formula (I):

wherein each R₁ is independently selected from alkyl, substituted alkyl,alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano (CN), and halogen; m and n are the numberof R₁ sidechains on their respective phenyl or naphthyl ring, and areindependently an integer from 0 to 6; X is selected from the groupconsisting of O, S, and Se; and a, b, and c are independently 0 or 1. Inthis regard, when a or b is 0, the exterior portion of the compound willbe a phenyl ring that may have up to 4 sidechains. When a or b is 1, theexterior portion of the compound will be a naphthyl ring that may haveup to 6 sidechains.

The term “alkyl” refers to a radical composed entirely of carbon atomsand hydrogen atoms which is fully saturated and of the formula—C_(n)H_(2n+1). The alkyl radical may be linear, branched, or cyclic.

The term “alkenyl” refers to a radical composed entirely of carbon atomsand hydrogen atoms which contains at least one carbon-carbon double bondthat is not part of an aryl or heteroaryl structure. The radical may belinear, branched, or cyclic.

The term “alkynyl” refers to a radical composed entirely of carbon atomsand hydrogen atoms which contains at least one carbon-carbon triplebond. The alkynyl radical may be linear, branched, or cyclic.

The term “aryl” refers to an aromatic radical composed entirely ofcarbon atoms and hydrogen atoms. When aryl is described in connectionwith a numerical range of carbon atoms, it should not be construed asincluding substituted aromatic radicals. For example, the phrase “arylcontaining from 6 to 10 carbon atoms” should be construed as referringto a phenyl group (6 carbon atoms) or a naphthyl group (10 carbon atoms)only, and should not be construed as including a methylphenyl group (7carbon atoms).

The term “heteroaryl” refers to an aromatic radical composed of carbonatoms, hydrogen atoms, and one or more heteroatoms. The carbon atoms andthe heteroatoms are present in a cyclic ring or backbone of the radical.The heteroatoms are selected from O, S, and N. Exemplary heteroarylradicals include thienyl and pyridinyl.

The term “alkoxy” refers to an alkyl radical which is attached to anoxygen atom, i.e. —O—C_(n)H_(2n+1).

The term “alkylthio” refers to an alkyl radical which is attached to asulfur atom, i.e. —S—C_(n)H_(2n+1).

The term “trialkylsilyl” refers to a radical composed of a tetravalentsilicon atom having three alkyl radicals attached to the silicon atom,i.e. —Si(R)₃. The three alkyl radicals may be the same or different.

The term “ketonyl” refers to a radical having a carbon atomdouble-bonded to an oxygen atom and single bonded to an alkyl orsubstituted alkyl group, i.e. —(C═O)—R. An exemplary ketonyl radical ismethylcarbonyl (—COCH₃).

The term “substituted” refers to at least one hydrogen atom on the namedradical being substituted with another functional group, such ashalogen, —CN, —NO₂, —COOH, and —SO₃H. An exemplary substituted alkylgroup is a perhaloalkyl group, wherein one or more hydrogen atoms in analkyl group are replaced with halogen atoms, such as fluorine, chlorine,iodine, and bromine. Besides the aforementioned functional groups, anaryl or heteroaryl group may also be substituted with alkyl or alkoxy.Exemplary substituted aryl groups include methylphenyl andmethoxyphenyl. Exemplary substituted heteroaryl groups includedodecylthienyl.

Generally, the alkyl and alkoxy groups each independently contain from 1to 30 carbon atoms, including from about 4 to about 16 carbon atoms.Similarly, the aryl groups independently contain from 6 to 30 carbonatoms.

When a, b, and c are 0, X is sulfur, and m and n are each 1, themolecule of Formula (I) is also formally known as adisubstituted-[1]benzothieno[3,2-b]benzothiophene. The[1]benzothieno[3,2-b]benzothiophene moiety (when m and n are each 0) maybe abbreviated herein as “BTBT”. For example, the semiconductor ofFormula (I) could be referred to as a disubstituted-BTBT.

In embodiments, the small molecule semiconductor has a band gap of fromabout 1.5 to about 3.5 eV, including from about 1.8 to about 2.8 eV.This large band gap typically means that the small moleculesemiconductor has better stability in air, when compared to apentacene-based semiconductor. The small molecule semiconductor has acrystalline or liquid crystalline structure. In specific embodiments,the semiconductor of Formula (I) is colorless in the visible region ofthe electromagnetic spectrum (i.e. from 390 nm to 750 nm). Colorlesssemiconductors not only provide excellent stability due to their largeband gaps, but also offer advantage in transparency for transparentdevice applications.

In some specific embodiments of Formula (I), a, b, and c are 0, and eachX is sulfur.

Five particular variations of the compound of Formula (I) arecontemplated by the present disclosure. In one variation, the smallmolecule semiconductor has the structure of Formula (II):

wherein R₂ and R₃ are independently selected from alkyl, substitutedalkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano, and halogen. On this semiconductorcompound of Formula (II), R₂ is located at the 2-position and R₃ islocated at the 7-position. Thus, the compound of Formula (II) could bereferred to as a 2,7-disubstituted-BTBT. Referring to Formula (I), thecompound of Formula (II) is obtained when a, b, and c are 0.

In some embodiments, the R₂ and R₃ are independently selected fromalkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano, and halogen. In some other embodiments,R₂ and R₃ are independently selected from alkyl and substituted alkyl,and the small molecule semiconductor is combined with specific polymerbinders to achieve high field-effect mobility. The polymer binders willbe explained further herein. The alkyl group may contain from about 4 toabout 30 carbon atoms, including from about 4 to about 16 carbon atoms.Exemplary alkyl groups include butyl, pentyl, hexyl, heptyl, octyl,decyl, dodecyl, tridecyl, hexadecyl, and the like. In some embodiments,the alkyl group has an odd number of carbon atoms; in other embodimentsthe alkyl group has an even number of carbon atoms. In particularembodiments, R₂ and R₃ are the same.

In another variation, the small molecule semiconductor has the structureof Formula (III):

wherein R₈, and R₉ are independently alkyl or substituted alkyl; andeach Ar is independently an arylene or heteroarylene group. Referringagain to Formula (I), the compound of Formula (III) is obtained when a,b, and c are 0; m and n are 1; and each R₁ is alkenyl or substitutedalkenyl. The alkyl group may contain from 1 to about 30 carbon atoms,including from about 4 to about 18 carbon atoms.

The term “arylene” refers to an aromatic radical composed entirely ofcarbon atoms and hydrogen atoms that can form single bonds with twodifferent atoms. An exemplary arylene group is phenylene (—C₆H₄—).

The term “heteroarylene” refers to an aromatic radical composed ofcarbon atoms, hydrogen atoms, and one or more heteroatoms, and that canform single bonds with two different atoms. The carbon atoms and theheteroatoms are present in a cyclic ring or backbone of the radical. Theheteroatoms are selected from O, S, and N. An exemplary heteroarylenegroup is 2,5-thienyl.

In a third variation, the small molecule semiconductor has the structureof Formula (IV):

wherein R₄ and R₅ are independently selected from alkyl, substitutedalkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano, and halogen; and j and k areindependently an integer from 0 to 6. Referring again to Formula (I),the compound of Formula (IV) is obtained when a and b are both 1, and cis 0. The R₄ and R₅ sidechains may be located on any carbon atom of theexterior naphthyl portions of the compound of Formula (IV).

In specific embodiments of Formula (IV), R₄ and R₅ are independentlyalkyl, j is 1, and k is 1.

In the next variation, the small molecule semiconductor has thestructure of Formula (V):

wherein R₆ and R₇ are independently selected from alkyl, substitutedalkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano, and halogen; and p and q areindependently an integer from 0 to 4. Referring again to Formula (I),the compound of Formula (V) is obtained when a and b are both 0, and cis 1.

In the final variation, the small molecule semiconductor has thestructure of Formula (VI):

wherein R₁₀ and R₁₁ are independently selected from alkyl, substitutedalkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano, and halogen; and a, b, and c areindependently 0 or 1.

In particular embodiments of Formula (VI), R₁₀ is halogen or cyano, andR₁₁ is alkyl, substituted alkyl, alkenyl, substituted alkenyl, orketonyl. In other embodiments, R₁₁ is halogen or cyano, and R₁₀ isalkyl, substituted alkyl, alkenyl, substituted alkenyl, or ketonyl.

Other specific variations on the small molecule semiconductor of Formula(I) are also shown here as Formulas (1)-(50):

wherein each R′ is independently alkyl or substituted alkyl containingfrom about 4 to about 20 carbon atoms, including from about 4 to about16 carbon atoms.

The semiconducting compounds of Formulas (2), (3), (7), (8), (9), (13),(14), (15), (20), (21), and (43) through (50) are also exemplarycompounds of Formula (II).

The semiconducting compounds of Formulas (2), (3), (13), (14), (15),(20), and (21) are also exemplary compounds of Formula (III).

The semiconducting compounds of Formulas (22), (23), (24), (25), (26),(27), (28), (29), (30), (31), (34), and (35) are also exemplarycompounds of Formula (IV).

The semiconducting compounds of Formulas (36), (37), (38), (39), and(40) are also exemplary compounds of Formula (V).

The semiconducting compounds of Formulas (4), (5), (10), (11), (12),(18), (19), (24), (25), (26), (27), (37), (38), (39), (41), and (42) arealso exemplary compounds of Formula (VI).

Various methods known in the arts can be used to make the small moleculesemiconductors described herein. For example, methods of producing thesmall molecule semiconductor of Formula (II) include reacting a2,7-dihalo-BTBT A with an alkyne to form a 2,7-dialkyn-1-yl-BTBT 1. Thisinitial reaction is illustrated below:

wherein X is a halogen, R_(a) is alkyl, Ph(PPh₃)₂Cl₂ isbis(triphenylphosphine) palladium(II) chloride, CuI is copper iodide,and iPr₂NH is diisopropylamine. As shown here, the two R_(a) groups areidentical. However, the two R_(a) groups can be different as well, forexample by using a blocking/protecting group on one of the X groups,performing a first reaction with a first alkyne to convert theunprotected X group, removing the blocking/protecting group, thensubsequently performing a second reaction with a second differentalkyne.

Next, the 2,7-dialkyn-1-yl-BTBT 1 can be reduced to a2,7-dialkyl-[1]benzothieno[3,2-b]benzothiophene 1a as depicted below:

wherein Pd/C is a palladium on carbon catalyst and THF istetrahydrofuran. Similar reactions can be performed for the otherpossible R_(a) substituents.

Methods for preparing compounds 1a also includes the reaction of the[1]benzothieno[3,2-b]-benzothiophene core B with a substituted acidchloride in presence of aluminum trichloride to form a 2,7-diketonylBTBT 2.

Next, the diketonyl BTBT 2 is deoxygenated using a modifiedWolff-Kishner reduction using hydrazine in the presence of potassiumhydroxide in diethylene glycol. This forms2,7-dialkyl-[1]benzothieno[3,2-b]benzothiophene 1b.

This 2-step method is particularly effective for short R_(b)substituents (C₂-C₈).

The small molecule semiconductor by itself has poor film-formingproperties, which is attributed to its crystalline or liquid crystallinenature. Thus, the semiconductor composition also comprises a polymerbinder, which allows a uniform film to be achieved, significantlyimproving device performance. The polymer binder can be considered asforming a matrix within which the small molecule semiconductor isdispersed.

Any suitable polymer can be used as the polymer binder for thesemiconductor composition. In some embodiments, the polymer is anamorphous polymer. The amorphous polymer may have a glass transitiontemperature less than the melting point temperature of the smallmolecule semiconductor. In other embodiments, the amorphous polymer hasa glass transition temperature greater than the melting pointtemperature of the small molecule semiconductor. In embodiments, thepolymer has a dielectric constant less than 4.5, preferably less than3.5, including less than 3.0, as measured at 60 Hz at room temperature.In embodiments, the polymer is selected from polymers containing only C,H, F, Cl, or N atoms. In some embodiments, the polymer is a low polaritypolymer, such as a hydrocarbon polymer or a fluorocarbon polymer withoutany polar groups. For example, polystyrene is an amorphous polymer andhas a dielectric constant about 2.6. A list of other low polaritypolymers includes but is not limited to the following:fluoropolyarylether, poly(p-xylylene), poly(vinyl toluene),poly(α-methyl styrene), poly(α-vinylnaphthalene), polyethylene,polypropylene, polyisoprene, poly(tetrafluoroethylene),poly(chlorotrifluoroethylene), poly(2-methyl-1,3-butadiene),poly(cyclohexyl methacrylate), poly(chlorostyrene), poly(4-methylstyrene), poly(vinyl, cyclohexane), polyphenylene,poly-p-phenylvinylidenes, poly(arylene ether), polyisobutylene,poly(2,6-dimethyl-1,4-phenylene ether), poly[1,1-(2-methylpropane)bis-(4-phenyl)carbonate], poly(a-a-a′-a′tetrafluoro-p-xylylene), fluorinated polyimide,poly(ethylene/tetrafluoroethylene),poly(ethylene/chlorotrifluoroethylene), fluorinated ethylene/propylenecopolymer, poly(styrene-co-a-methyl styrene), poly(styrene/butadiene),poly(styrene/2,4-dimethylstyrene), CYTOP, poly(propylene-co-1-butene),poly(styrene-co-vinyl toluene),poly(styrene-block-butadiene-block-styrene),poly(styrene-block-isoprene-block-styrene), terpene resin,poly(N-vinylcarbazole), polycarbazole, polytriarylamine, and the like.

It has been found that the mobility of the semiconducting layer formedby the semiconductor composition can be affected by the combination ofsmall molecule semiconductor with certain polymers. The compounds ofFormula (I) can be combined with many different polymers. In someparticular embodiments, the polymer binder is a styrene-based polymer.

Styrene-based polymers contain a repeating unit derived from a styrenemonomer of Formula (a):

wherein R^(g), R^(h), R^(j), and R^(k) are independently selected fromhydrogen, halogen, and C₁-C₂₀ alkyl; and n is an integer from 0 to 5.The styrene monomer can be styrene (R^(g), R^(h), and R^(j) are allhydrogen, n=0), alpha-methyl styrene (R^(g) is methyl, R^(h) and R^(j)are hydrogen, n=0), or 4-methyl styrene (R^(g), R^(h), and R^(j) are allhydrogen, n=1, R^(k) is methyl in the 4-position). The term“styrene-based polymer” is intended to encompass both homopolymers andcopolymers. The term “copolymer” is intended to encompass random,alternative, and block copolymers.

In other particular embodiments, the polymer binder is anarylamine-based polymer. An arylamine-based polymer has a repeating unitderived from a monomer having the structure of Formula (b), Formula (c)or Formula (d):

wherein R^(m), R^(n), R^(p), R^(q), and R^(r) are independently selectedfrom hydrogen, halogen, C₁-C₂₀ alkyl, and aryl; p′ and q′ areindependently an integer from 0 to 5; and R^(w) is selected from C₁-C₂₀alkyl, aryl, and substituted aryl. The term “arylamine-based” polymersis intended to encompass poly(N-vinyl carbazole), polycarbazole, andtriarylamine-based polymers.

In specific embodiments, the styrene-based polymer and thearylamine-based polymer include polystyrene, poly(α-methyl styrene),poly(4-methyl styrene), poly(vinyl toluene), poly(α-methylstyrene-co-vinyl toluene), poly(styrene-block-butadiene-block-styrene),poly(styrene-block-isoprene-block-styrene), a terpene resin,poly(styrene-co-2,4-dimethylstyrene), poly(chlorostyrene),poly(styrene-co-α-methyl styrene), poly(styrene/butadiene),poly(N-vinylcarbazole), polycarbazole, and polytriarylamines. It shouldbe noted that one or more polymer binders can be used in thesemiconductor composition.

The compound of Formula (II) works best when combined with the polymerbinders discussed above, particularly, the styrene-based polymer or thearylamine-based polymer described above.

In more specific embodiments, the polymer binder is a styrene-basedpolymer. In particular embodiments, the styrene-based polymer has aweight average molecular weight of from about 40,000 to about 2,000,000.In some embodiments, the styrene-based polymer has a molecular weight offrom about 100,000 to about 1,000,000. In one preferred embodiment, thepolymer binder is polystyrene, poly(alpha-methyl styrene), orpoly(4-methyl styrene) having a weight average molecular weight of fromabout 40,000 to about 2,000,000.

The compounds of Formulas (III), (IV), (V), and (VI) can generally becombined with any polymer binder. Exemplary polymer binders include thepolymer binders discussed above, and other polymers such as poly(vinylcinnamate), polysiloxanes, polypyrroles, polyacrylates,polymethacrylates, polyesters, and mixtures thereof. The polymers mayhave a weight average molecular weight of from about 10,000 to about2,000,000, including from about 40,000 to about 1,000,000.

The weight ratio of the small molecule semiconductor of Formula (I) tothe polymer binder may be from about 99:1 to about 1:3, including fromabout 10:1 to about 1:2, from about 5:1 to about 2:3, or from about 3:2to about 3:4. In some embodiments, the weight ratio of the smallmolecule semiconductor of Formula (I) to the polymer binder is around1:1. The weight ratio of the small molecule semiconductor of Formula(II) to the styrene-based polymer binder is desirably from about 3:2 toabout 2:3, and works optimally at a ratio of about 1:1.

The semiconductor composition may further comprise a solvent in whichthe small molecule semiconductor and the polymer binder are soluble.Exemplary solvents used in the solution may include chlorinated solventssuch as chlorobenzene, chlorotoluene, dichlorobenzene, dichloroethane,chloroform, trichlorobenzene, and the like; alcohols and diols such aspropanol, butanol, hexanol, hexanediol, etc.; hydrocarbons or aromatichydrocarbons such as hexane, heptane, toluene, decalin, xylene, ethylbenzene, tetrahydronaphthalene, methyl nanphthalene, mesitylene,trimethyl benzene, etc.; ketones such as acetone, methyl ethyl ketone,etc.; acetates, such as ethyl acetate; pyridine, tetrahydrofuran, andthe like.

The small molecule semiconductor and the polymer binder are from about0.05 to about 20 weight percent of the semiconductor composition,including from about 0.1 to about 10 weight percent of the semiconductorcomposition, or from about 0.1 to about 1.0 weight percent of thesemiconductor composition.

In embodiments, the semiconductor composition comprising the smallmolecule semiconductor and the polymer binder may have a viscosity offrom about 1.5 centipoise (cps) to about 100 cps, including from about 2to about 20 cps. The use of a high molecular weight polymer binder willincrease the viscosity of the semiconductor composition. As a result, itwill help to form a uniform semiconductor layer upon using solutiondeposition techniques such as inkjet printing and spin coating.

Bottom-gate TFTs may be advantageous because they are generally simplerto fabricate. However, previous semiconductor/polymer composite systemshave only achieved high mobility in top-gate devices. When thesemiconductor composition of the present disclosure is utilized, highmobility can also be achieved in bottom-gate devices like those shown inFIGS. 1-3.

The semiconducting layer may be formed in an electronic device usingconventional processes known in the art. In embodiments, thesemiconducting layer is formed using solution depositing techniques.Exemplary solution depositing techniques include spin coating, bladecoating, rod coating, dip coating, screen printing, ink jet printing,stamping, stencil printing, screen printing, gravure printing,flexography printing, and the like.

After being deposited, the semiconductor composition is optionallythermally treated (for example, by drying or annealing) at an elevatedtemperature which is lower than the melting point of the small moleculesemiconductor used in the semiconductor composition. Depending on thesmall molecule semiconductor used, the temperature of the thermaltreatment may vary. For example, the thermal treatment may be carriedout at a temperature of less than 200° C., less than 150° C., or lessthan 100° C. Generally, the semiconductor layer will not undergo athermal treatment process having a temperature higher than the meltingpoint of the small molecule semiconductor. In some embodiments,particularly those which use the small molecule semiconductor of Formula(I), there is absent of an annealing step during the fabrication of asemiconductor layer from the semiconductor composition. Annealing at atemperature higher than the melting point of the small moleculesemiconductor would cause significant phase separation of the smallmolecule semiconductor and the polymer binder, as well as increasing theaverage crystal size of the small molecule semiconductor. As a result,the electronic device would show poor electrical performance.

In the bottom-gate and top-gate embodiments shown in FIGS. 1-4, thealignment layer is laid down before the semiconducting layer. Thealignment treatment can be performed on the surface of the alignmentlayer before the source electrode, drain electrode, and semiconductinglayer are deposited. In the top-gate embodiment of FIG. 4, the gatedielectric layer and the gate electrode are subsequently deposited uponthe semiconducting layer.

In some embodiments, the small molecule semiconductor is a liquidcrystalline material, or in other words the semiconductor is a liquidcrystalline compound (e.g. showing at least a liquid crystalline phasesuch as nematic or smectic phase) at an elevated temperature. Annealingwould help to achieve macroscopic alignment of the small moleculesemiconductor upon an alignment layer. In embodiments, the annealing isconducted at a temperature below the liquid crystal phase-isotropicphase transition temperature of the small molecule semiconductor. Insome embodiments, annealing is performed at a temperature higher thanthe crystal-liquid crystal phase transition temperature of the smallmolecule semiconductor. In other embodiments, annealing is performed ata temperature below the crystal-liquid crystal phase transitiontemperature.

In particular embodiments, the small molecule semiconductor iscrystalline, particularly at room temperature, and has an averagecrystal size in the semiconducting layer of 100 nanometers or less. Inspecific embodiments, the average crystal size is 50 nanometers or less.In more specific embodiments, the average crystal size is 35 nanometersor less. The crystalline small molecule semiconductor generally has acrystal size greater than 5 nanometers. The average crystal size can bemeasured using methods such as X-ray diffraction, transmission electronmicroscopy (TEM), scanning electron microscopy (SEM), atomic forcemicroscopy (AFM), etc. The measurement of the average crystal size isexpressed as the diameter of a spherical volume. However, this shouldnot be construed as requiring the crystals of the small moleculesemiconductor to have a particular morphology or shape.

The semiconducting layer formed using the semiconductor composition canbe from about 5 nanometers to about 1000 nanometers deep, including fromabout 20 to about 100 nanometers in depth. In certain configurations,such as the configurations shown in FIG. 1, the semiconducting layercompletely covers the source and drain electrodes.

The performance of a TFT can be measured by mobility. The mobility ismeasured in units of cm²/V·sec; higher mobility is desired. Theresulting TFT including the alignment layer and semiconducting layer ofthe present disclosure may have a field effect mobility of at least 0.8cm²/V·sec, including at least 0.9 cm²/V·sec, or at least 1.0 cm²/V·sec.The TFT of the present disclosure may have a current on/off ratio of atleast 10⁵, including at least 10⁶.

The thin film transistor generally also includes a substrate, anoptional gate electrode, source electrode, drain electrode, and adielectric layer in addition to the alignment layer and thesemiconducting layer.

The substrate may be composed of materials including but not limited tosilicon, glass plate, plastic film or sheet. For structurally flexibledevices, plastic substrate, such as for example polyester,polycarbonate, polyimide sheets and the like may be preferred. Thethickness of the substrate may be from about 10 micrometers to over 10millimeters with an exemplary thickness being from about 50 to about 100micrometers, especially for a flexible plastic substrate and from about0.5 to about 10 millimeters for a rigid substrate such as glass orsilicon.

The dielectric layer generally can be an inorganic material film, anorganic polymer film, or an organic-inorganic composite film. Examplesof inorganic materials suitable as the dielectric layer include siliconoxide, silicon nitride, aluminum oxide, barium titanate, bariumzirconium titanate and the like. Examples of suitable organic polymersinclude polyesters, polycarbonates, poly(vinyl phenol), polyimides,polystyrene, polymethacrylates, polyacrylates, epoxy resin and the like.The thickness of the dielectric layer depends on the dielectric constantof the material used and can be, for example, from about 10 nanometersto about 500 nanometers. The dielectric layer may have a conductivitythat is, for example, less than about 10⁻¹² Siemens per centimeter(S/cm). The dielectric layer is formed using conventional processesknown in the art, including those processes described in forming thegate electrode.

The gate electrode is composed of an electrically conductive material.It can be a thin metal film, a conducting polymer film, a conductingfilm made from conducting ink or paste, or the substrate itself, forexample heavily doped silicon. Examples of gate electrode materialsinclude but are not restricted to aluminum, gold, silver, chromium,indium tin oxide, conductive polymers such as polystyrenesulfonate-doped poly(3,4-ethylenedioxythiophene) (PSS-PEDOT), andconducting ink/paste comprised of carbon black/graphite. The gateelectrode can be prepared by vacuum evaporation, sputtering of metals orconductive metal oxides, conventional lithography and etching, chemicalvapor deposition, spin coating, casting or printing, or other depositionprocesses. The thickness of the gate electrode ranges for example fromabout 10 to about 200 nanometers for metal films and from about 1 toabout 10 micrometers for conductive polymers. Typical materials suitablefor use as source and drain electrodes include those of the gateelectrode materials such as aluminum, gold, silver, chromium, zinc,indium, conductive metal oxides such as zinc-gallium oxide, indium tinoxide, indium-antimony oxide, conducting polymers and conducting inks.Typical thicknesses of source and drain electrodes are, for example,from about 40 nanometers to about 1 micrometer, including more specificthicknesses of from about 100 to about 400 nanometers.

Typical materials suitable for use as source and drain electrodesinclude those of the gate electrode materials such as gold, silver,nickel, aluminum, platinum, conducting polymers, and conducting inks. Inspecific embodiments, the electrode materials provide low contactresistance to the semiconductor. Typical thicknesses are about, forexample, from about 40 nanometers to about 1 micrometer with a morespecific thickness being about 100 to about 400 nanometers. The OTFTdevices of the present disclosure contain a semiconductor channel. Thesemiconductor channel width may be, for example, from about 5micrometers to about 5 millimeters with a specific channel width beingabout 100 micrometers to about 1 millimeter. The semiconductor channellength may be, for example, from about 1 micrometer to about 1millimeter with a more specific channel length being from about 5micrometers to about 100 micrometers.

The source electrode is grounded and a bias voltage of, for example,about 0 volt to about 80 volts is applied to the drain electrode tocollect the charge carriers transported across the semiconductor channelwhen a voltage of, for example, about +10 volts to about −80 volts isapplied to the gate electrode. The electrodes may be formed or depositedusing conventional processes known in the art.

If desired, a barrier layer may also be deposited on top of the TFT toprotect it from environmental conditions, such as light, oxygen andmoisture, etc. which can degrade its electrical properties. Such barrierlayers are known in the art and may simply consist of polymers.

The various components of the OTFT may be deposited upon the substratein any order. Generally, however, the gate electrode and thesemiconducting layer should both be in contact with the gate dielectriclayer. In addition, the source and drain electrodes should both be incontact with the semiconducting layer. The phrase “in any order”includes sequential and simultaneous formation. For example, the sourceelectrode and the drain electrode can be formed simultaneously orsequentially. The term “on” or “upon” the substrate refers to thevarious layers and components with reference to the substrate as beingthe bottom or support for the layers and components which are on top ofit. In other words, all of the components are on the substrate, eventhough they do not all directly contact the substrate. For example, boththe dielectric layer and the semiconductor layer are on the substrate,even though one layer is closer to the substrate than the other layer.The resulting TFT has good mobility and good current on/off ratio.

The following examples are for purposes of further illustrating thepresent disclosure. The examples are merely illustrative and are notintended to limit devices made in accordance with the disclosure to thematerials, conditions, or process parameters set forth therein. Allparts are percentages by volume unless otherwise indicated.

EXAMPLES Comparative Example 1

An n-doped silicon wafer was provided as a substrate. A silicon oxidedielectric layer was thermally grown on the wafer. The dielectric layerwas grown to a thickness of 200 nm. The surface of the dielectric layerwas modified with hexamethyldisilazane (HMDS). The HMDS layer was about0.3 nm thick.

A semiconductor solution was formed by dissolving 15 mg of polystyreneand 15 mg of 2,7-ditridecyl[1]benzothieno[3,2-b]benzothiophene into 2grams of chlorobenzene solvent. The semiconductor solution was spincoated on the modified substrate to form a uniform film. The film wasdried for 30 minutes at 70-80° C. to form the semiconducting layer. Goldsource and drain electrodes were vacuum evaporated on top of thesemiconducting layer to finish the device. Several devices were made.

Comparative Example 2

Devices were formed as described in Comparative Example 1. However, thesurface of the dielectric layer was modified with octyltrichlorosilane(OTS-8) instead. The OTS-8 layer was about 0.7 nm thick.

Testing of Comparative Examples

The transistors formed in the two Comparative Examples werecharacterized with a KEITHLEY® 4200 Semiconductor CharacterizationSystem at ambient conditions. At least 10 devices were evaluated. Thehighest mobility measured was 0.77 cm²/V·s. The average mobility of thedevices was about 0.48 cm²/V·sec for the devices of Comparative Example1 (HMDS-modified), and about 0.53 cm²/V·sec for the devices ofComparative Example 2 (OTS-8 modified).

Example 1

An n-doped silicon wafer was provided as a substrate. A silicon oxidedielectric layer was thermally grown on the wafer. The dielectric layerwas grown to a thickness of 200 nm. The surface of the dielectric layerwas modified with OTS-8. The OTS-8 layer was about 0.7 nm thick. TheOTS-8 layer was then gently rubbed in one direction with velvet cloth ina rubbing machine at 1000 rpm.

A semiconductor solution was formed by dissolving 15 mg of polystyreneand 15 mg of 2,7-ditridecyl[1]benzothieno[3,2-b]benzothiophene into 2grams of chlorobenzene solvent. The semiconductor solution was spincoated on the modified substrate to form a uniform film. The film wasdried for 30 minutes at 70-80° C. to form the semiconducting layer.

Gold source and drain electrodes were vacuum evaporated on top of thesemiconducting layer so that the channel length was along the rubbingdirection. Several devices were made.

The transistors were characterized with a KEITHLEY® 4200 SemiconductorCharacterization System at ambient conditions. At least 10 devices wereevaluated. The highest mobility measured was 1.5 cm²/V·s. The averagemobility of the devices was about 0.9 cm²/V·s. Compared to theComparative Examples, the average mobility was improved by a factor ofabout two, as was the highest mobility.

It will be appreciated that variants of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be combined intomany other different systems or applications. Various presentlyunforeseen or unanticipated alternatives, modifications, variations orimprovements therein may be subsequently made by those skilled in theart which are also intended to be encompassed by the following claims.

1. An electronic device comprising: a semiconducting layer comprising asmall molecule semiconductor and a polymer binder; and an alignmentlayer in contact with the semiconductor layer.
 2. The electronic deviceof claim 1, wherein the alignment layer has a thickness of from about0.2 nanometers to about 1 micrometer.
 3. The electronic device of claim1, wherein the alignment layer is formed from a polyimide, a poly(vinylcinnamate), an azobenzene polymer, a styrene-based polymer, or anorganosilane agent of Formula (A):(L)_(t)-[SiR_(m)(R′)_(4-m-t)]_(v)  Formula (A) wherein R is alkyl oraryl; R′ is halogen or alkoxy; m is an integer from 1 to 4; L is alinking atom; t is 0 or 1; and v indicates the number oftrisubstitutedsilyl groups on the linking atom.
 4. The electronic deviceof claim 1, wherein the small molecule semiconductor is a liquidcrystalline compound.
 5. The electronic device of claim 1, wherein thesmall molecule semiconductor has the structure of Formula (I):

wherein each R₁ is independently selected from alkyl, substituted alkyl,alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano, and halogen; m and n are the number of R₁sidechains on their respective phenyl or naphthyl ring, and areindependently an integer from 0 to 6; X is selected from the groupconsisting of O, S, and Se; and a, b, and c are independently 0 or
 1. 6.The electronic device of claim 5, wherein the small moleculesemiconductor has the structure of Formula (II):

wherein R₂ and R₃ are independently selected from alkyl, substitutedalkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano, and halogen.
 7. The electronic device ofclaim 5, wherein the small molecule semiconductor has the structure ofFormula (III);

wherein R₈, and R₉ are independently alkyl or substituted alkyl; andeach Ar is independently an arylene or heteroarylene group.
 8. Theelectronic device of claim 5, wherein the small molecule semiconductorhas the structure of Formula (IV):

wherein R₄ and R₅ are independently selected from alkyl, substitutedalkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano, and halogen; and j and k areindependently an integer from 0 to
 6. 9. The electronic device of claim5, wherein the small molecule semiconductor has the structure of Formula(V):

wherein R₆ and R₇ are independently selected from alkyl, substitutedalkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano, and halogen; and p and q areindependently an integer from 0 to
 4. 10. The electronic device of claim5, wherein the small molecule semiconductor has the structure of Formula(VI):

wherein R₁₀ and R₁₁ are independently selected from alkyl, substitutedalkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl,substituted aryl, heteroaryl, substituted heteroaryl, alkoxy, alkylthio,trialkylsilyl, ketonyl, cyano, and halogen; and a, b, and c areindependently 0 or
 1. 11. The electronic device of claim 1, wherein thepolymer binder is a styrene-based polymer or an arylamine-based polymer.12. The electronic device of claim 11, wherein the polymer binder ispolystyrene, poly(α-methyl styrene), poly(4-methyl styrene),poly(alpha-methyl styrene-co-vinyl toluene),poly(styrene-block-butadiene-block-styrene),poly(styrene-block-isoprene-block-styrene), poly(vinyl toluene), aterpene resin, poly(styrene-co-2,4-dimethylstyrene),poly(chlorostyrene), poly(styrene-co-α-methyl styrene),poly(styrene-co-butadiene), polycarbazole, a polytriarylamine, orpoly(N-vinylcarbazole).
 13. The electronic device of claim 11, whereinthe polymer binder is a styrene-based polymer having a weight averagemolecular weight of from about 40,000 to about 2,000,000.
 14. Theelectronic device of claim 1, wherein the weight ratio of the smallmolecule semiconductor to the polymer binder is from about 99:1 to about1:3.
 15. A thin film transistor comprising: a gate electrode, a sourceelectrode, and a drain electrode, the source electrode and the drainelectrode defining a transistor channel; a gate dielectric layer; asemiconductor layer comprising a small molecule semiconductor and apolymer binder; and an alignment layer in contact with the semiconductorlayer; wherein the small molecule semiconductor is aligned along thedirection of the transistor channel.
 16. The thin film transistor ofclaim 15, wherein the semiconducting layer has a field-effect mobilityof at least 0.8 cm²/V·sec.
 17. The thin film transistor of claim 15,wherein the alignment layer is located between the semiconductor layerand the gate dielectric layer.
 18. A method for forming a thin filmtransistor device, comprising: depositing an alignment layer on asubstrate; aligning the alignment layer in a transistor channeldirection; depositing a semiconducting layer on the alignment layer;depositing a source electrode and a drain electrode, wherein the sourceelectrode and the drain electrode define a transistor channel.
 19. Themethod of claim 18, wherein the alignment layer is aligned by rubbingthe alignment layer in the transistor channel direction.
 20. The methodof claim 18, wherein the alignment layer is formed from a polyimide, apoly(vinyl cinnamate), or an azobenzene polymer; and the alignment layeris aligned by irradiating the alignment layer with linearly polarizedlight.